add --without-ssh1 option to configure

Allows disabling support for SSH protocol 1.
diff --git a/auth1.c b/auth1.c
index 5038828..5073c49 100644
--- a/auth1.c
+++ b/auth1.c
@@ -12,6 +12,8 @@
 
 #include "includes.h"
 
+#ifdef WITH_SSH1
+
 #include <sys/types.h>
 
 #include <stdarg.h>
@@ -438,3 +440,5 @@
 	packet_send();
 	packet_write_wait();
 }
+
+#endif /* WITH_SSH1 */